There are many desirable features associated with fluorescent lamps, compared to incandescent lamps. For example, fluorescent lamps typically use substantially less electrical power and produce equal or greater illumination. The lower power consumption is desirable to all users but is particularly important in those areas of the world with insufficient power generation capacity.
One of the difficulties associated with fluorescent lamps is starting or igniting them. Starting the lamp requires both a separate starter and the coalescence of various factors including the instantaneous voltage, timing and temperature, all of which have been discussed more completely in the '007 Application referenced above. The fluorescent starter described in the '007 Application is very effective in reliably igniting a fluorescent lamp and in eliminating many of the variables which have previously inhibited reliable starting.
One disadvantage associated with fluorescent lamps relates to controlling their illumination intensity. The typical fluorescent dimmer uses an electronic ballast which delivers a continuous current to the cathodes of the fluorescent lamp to maintain the cathodes in a heated condition during dimming. During normal operation, the current flowing between the cathodes in the fluorescent lamp is adequate to maintain the cathodes in an heated condition, thereby assuring reliable ignition with each half-cycle of applied AC power at full intensity operation. However, when the illumination intensity is reduced by reducing the voltage or current between the cathodes, the amount of cathode heating is reduced. If the cathodes are not heated sufficiently, the lamp will not reliably ignite with each half-cycle of applied AC power. Therefore, the electronic ballast must supply a separate cathode heating current while the voltage or current between the cathodes is varied to control the illumination intensity.
The necessity to control the heating current through the cathodes separately from the ignition or illumination voltage applied between the lamp cathodes has caused prior art dimmer controls and electronic ballasts to be relatively expensive and complex in construction. Furthermore, prior art fluorescent lamp dimmers are additional components used with the ordinarily lamp starters. Consequently, it is relatively costly to provide dimming capabilities for fluorescent lamps, and the added cost is one of the reasons that dimming controls for fluorescent lamps are not more widely used or accepted.
It is with respect to this and other background information that the present invention has evolved.